This application claims the benefit of Korean Patent Application No. 2002-6753, filed Feb. 6, 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus and a method thereof, and more particularly, to an image forming apparatus for and a method of controlling an image concentration.
2. Description of the Related Art
FIG. 1 illustrates an overall arrangement of a conventional image forming apparatus disclosed in U.S. Pat. No. 4,564,287. Referring to FIG. 1, the conventional image forming apparatus includes a photosensitive drum 1, a primary charger 2, a secondary charger 3, an entire surface exposure lamp 4, a potentiometer 7, a developing roller 5 of a developing unit, a transfer charger 28, a cleaner blade 35, and a discharger 29.
The photosensitive drum 1 is pre-discharged by the pre-discharge charger 29, and then, an entire surface of the photosensitive drum 1 is uniformly charged. A reflected light beam illuminated by an original exposure lamp 11 and reflected from an original image 10 is radiated on the photosensitive drum 1 through mirrors 12 and 13. In this case, an AC corona discharge or corona discharge having an opposite polarity to that of the primary charger 2 is performed by the secondary charger 3 to form an electrostatic latent image on the photosensitive drum 1 in accordance with the original image 10.
The entire surface of the photosensitive drum 1 is then exposed by the entire surface exposure lamp 4, so that the electrostatic latent image having a high contrast is formed. This latent image is then toner developed by the developing roller 5.
The transfer charger 28 is then operated to transfer the developed image to a recoding paper sheet (not shown). A blank exposure lamp 6 preventing an adhesion of excessive toner to the photosensitive drum 1 is disposed above the secondary charger 3 to form light color areas and dark color areas on the photosensitive drum 1 under a control with standard image formation conditions.
The potentiometer 7 measuring a surface potential of the photosensitive drum 1 is disposed between the entire surface exposure lamp 4 and the developing roller 5. A signal from the potentiometer 7 is supplied to an A/D converter 9 through a potential measurement circuit 8 and is converted into a digital signal by the A/D converter 9. This digital signal is supplied to a microcomputer 15.
An output from the microcomputer 15 is supplied to a D/A converter 16 and is connected to a light control circuit 17, a first high voltage control circuit 18, a second high voltage control circuit 19, a transfer control circuit 24, a pre-discharge control circuit 25, and a DC development bias control circuit 20. In an operation section 40 various key-in operations and display operations are performed.
The light control circuit 17 controls the original exposure lamp 11 through a lamp regulator 14. The first and second high voltage control circuits 18 and 19 are connected to the primary charger 2 and the secondary charger 3 through first and second high voltage transformers 21 and 22, respectively, to control respective charges of the primary and secondary chargers 2 and 3. The transfer control circuit 24 is connected to the transfer charger 28 through the transfer high voltage transformer 26.
The pre-discharge control circuit 25 is connected to the pre-discharge charger 29 through a pre-discharge high voltage transformer 27. An output from the DC development bias control circuit 20 is connected to an AC development bias control circuit 23, and an output from the AC development bias control circuit 23 is applied to the developing roller 5. A standard white board 38 is used to control a light amount of the original exposure lamp 11.
In the above conventional image forming apparatus, the surface potential of the photosensitive drum 1 is measured by the potentiometer 7, and a development bias of the developing roller 5 and charge potentials of the primary and second chargers 2, 3 are adjusted in accordance with a result of measurement of the surface potential of the photosensitive drum 1. However, since only the surface potential of the image forming apparatus is measured in prior art, a variation in an image concentration caused by a variation in the thickness of the photosensitive body cannot be measured, and thus a uniform image concentration cannot be achieved.
To solve the above and other problems, it is an object of the present invention to provide an image forming apparatus for preventing a decrease in an image concentration caused by a variation in a thickness of a photosensitive body.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, according to an embodiment of the present invention,] there is provided an image forming apparatus. The apparatus includes a photosensitive body on which an electrostatic latent image for an image is formed, a charger charging the photosensitive body, a developing unit developing the electrostatic latent image of the photosensitive body, a measuring unit measuring a charge current flowing through the photosensitive body from the charger, a comparator comparing the charge current with a reference current, and a controller controlling a developing unit control variable so as to compensate for a variation in a thickness of the photosensitive body according to an output of the comparator.
According to an aspect of the present invention, the developing unit control variable is a development bias of the developing unit or a development vector, which is a difference between the development bias and an exposure potential of an exposure unit.
In order to achieve the above and other objects, according to another embodiment of the present invention, there is provided a method of compensating for the development mass per area caused by the thickness of the photosensitive body of the image forming apparatus. The method includes measuring a charge current Ii of the photosensitive body, comparing the measured charge current Ii with a first reference current Irmin of the photosensitive body, comparing the measured charge current Ii with a second reference current Irmax in a case that the measured charge current Ii is larger than the first reference current Irmin, and replacing the photosensitive body with a new one in a case that the measured charge current Ii is larger than the second reference current Irmax, and performing an operation of the developing unit control variable and controlling the developing unit in an opposite case that the measured charge current Ii is smaller than the second reference current Irmax.
In the replacing of the photosensitive body with the new one, a command replacing the photosensitive body is transferred to a display.
According to another aspect of the present invention, in order to compensate for a variation in development mass per area caused by the thickness of the photosensitive body, the development mass per area is compensated by measuring the charge current of the photosensitive body and correcting the development bias in a case that the measured charge current is larger than a minimum reference current, and a high quality image can be obtained during a life span of a new photosensitive body by informing a user whether the photosensitive body has to be replaced in a case that the measured charge current is larger than a maximum reference current.